ScrumbleShip is the most accurate space combat simulation devised to date. Gather resources, construct a capital ship out of individual blocks, then pilot it with AI or human help against other players.

Quick video showing off the performance improvements. On my machine, I've gone from seeing ~300,000 voxels at 20-30fps to seeing nearly 1 million at 40-50fps. And there's still a semi-easy 10-15fps I haven't chased yet!